If you’ve more than one contactless card (which includes your Oyster card, contactless Barclaycard, Barclays debit card, any other contactless card, or a building pass), we recommend you keep them separate, and only touch one card on the reader when touching in and out.
If more than one contactless card is touched against the payment reader at the same time, it may result in card clash. When this happens, the ticket gate won't open or a red light will appear, and you may end up paying for your travel with the wrong card. Alternatively, the reader may read, for example, your Oyster card when you touch in, and your Barclaycard when you touch out. In this situation, you'd be charged a maximum fare on both of your cards, as the two parts of your journey wouldn't be linked together on one card.